[MIS19-P28] Variability of hemipelagic and event depositions in the Beppu Bay during Holocene
Keywords:Beppu Bay, Sediment, Detrital component, X-ray diffraction analysis
As a result, quartz / feldspars ratio of the Beppu Bay sediment was within the range of surface soils in the drainage of Ohno River and Oita River. Detailed examination of peak shape of feldspar in X-ray diffractogram suggests grain size dependency of feldspar composition. Feldspars in finer materials showed more “mafic” composition suggesting that fine materials are dominantly supplied from Oita River drainage and / or mafic rock is more easily weathered and forms fine materials. We also applied statistical unmixing of mineral assemblage using PARAFAC algorithm on XRD profiles. Statistically distinguished subcomponents could be attributed to biogenic subcomponents, detrital subcomponents from the Ohno and Oita Rivers in hemipelagic mud as well as two detrital subcomponents in event sands with different origin.
Temporal variation of these statistical subcomponents in hemipelagic mud suggests that vegetation and / or land use change in the drainage area affected the relative importance of suspension loads from the Ohno River associated with the increase of detrital flux for the last 3,000 yrs. Composition of event sands also shows a consistent compositional change characterized by the relative increase of contribution from sandy material of the Ohno River bed. Increase in surface erosion in the Ohno River drainage may have been responsible for increases of fine and coarse materials supply and development of the delta at the river mouth.